Simplify installation instructions (#347)
Simplify installation instructions (#347)

Now that PySB and its dependencies including BioNetGen are on
Anaconda, the installation procedure is much simpler.

I've also added Cython to the list of recommended packages.
LoLab-VU/pysb,alubbock/pysb,jmuhlich/pysb,johnbachman/pysb,LoLab-VU/pysb,johnbachman/pysb,pysb/pysb